Surface roughness for flowable CVD film

ABSTRACT

Methods for forming a smooth ultra-thin flowable CVD film by using a surface treatment on a substrate surface before flowable CVD film deposition improves the uniformity and overall film smoothness. The flowable CVD film can be cured by any suitable curing process to form a smooth flowable CVD film.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.62/877,431, filed Jul. 23, 2019, the entire disclosure of which ishereby incorporated by reference herein.

TECHNICAL FIELD

The present disclosure relates generally to methods of depositing thinfilms. In particular, the disclosure relates to processes for improvingsurface roughness for flowable chemical vapor deposition (CVD) thinfilms.

BACKGROUND

In microelectronics device fabrication there is a need to fill narrowtrenches having aspect ratios (AR) greater than 10:1 with no voiding formany applications. One application is for shallow trench isolation(STI). For this application, the film needs to be of high qualitythroughout the trench (having, for example, a wet etch rate ratio lessthan two) with very low leakage. As the dimensions of the structuresdecrease and the aspect ratios increase post curing methods of the asdeposited flowable CVD films become difficult. Resulting in films withvarying composition throughout the filled trench.

Conventional plasma-enhanced chemical vapor deposition (PECVD) ofdielectric films form a “mushroom shape” film on top of the narrowtrenches. This is due to the inability of the plasma to penetrate intothe deep trenches. The results in pinching-off the narrow trench fromthe top; forming a void at the bottom of the trench.

Flowable chemical vapor deposition (FCVD) has been widely used inadvanced generations of semiconductor devices. As feature sizesdecrease, the required gap fill volume of FCVD films can be reducedgreatly compared to previous nodes (e.g. <500 Å or <300 Å). It iscritical, but challenging, to deposit thin FCVD films having a smoothand uniform surface as well as high gap fill performance. Accordingly,there is a need for method of improving surface roughness for flowableCVD films.

SUMMARY

One or more embodiments of the disclosure are directed to processingmethods. In one embodiment, a process method comprises pre-treating asubstrate surface with a plasma to form a smooth pre-treated substratesurface; forming a flowable CVD film on the pre-treated substratesurface by exposing the pre-treated substrate surface to a precursor anda reactant; and curing the flowable CVD film.

Additional embodiments of the disclosure are directed to processingmethods comprising pre-treating a substrate surface with a plasma toform a smooth pre-treated substrate surface; flowing trisilylamine (TSA)over the pre-treated substrate, followed by flowing ammonia (NH₃) toform a treated substrate; forming a flowable CVD film on the treatedsubstrate by exposing the treated substrate to a precursor and areactant, the flowable CVD film having a thickness in a range of about 5nm to about 50 nm; and curing the flowable CVD film.

Further embodiments of the disclosure are directed to processing methodscomprising pre-treating a substrate surface with a plasma to form asmooth pre-treated substrate surface; flowing trisilylamine (TSA) overthe pre-treated substrate, followed by flowing ammonia (NH₃) and oxygen(O₂) to form a flowable CVD film having a thickness in a range of about5 nm to about 50 nm; eliminating oxygen (O₂); turning off the flow ofammonia (NH₃), while continuing to flow TSA over the treated substrate;and curing the flowable CVD film.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 shows a cross-sectional view of a substrate in accordance withone or more embodiments of the disclosure; and

FIG. 2 shows a cross-sectional view of a substrate in accordance withone or more embodiments of the disclosure.

DETAILED DESCRIPTION

Before describing several exemplary embodiments of the invention, it isto be understood that the invention is not limited to the details ofconstruction or process steps set forth in the following description.The invention is capable of other embodiments and of being practiced orbeing carried out in various ways.

A “substrate” as used herein, refers to any substrate or materialsurface formed on a substrate upon which film processing is performedduring a fabrication process. For example, a substrate surface on whichprocessing can be performed include materials such as silicon, siliconoxide, strained silicon, silicon on insulator (SOI), carbon dopedsilicon oxides, amorphous silicon, doped silicon, germanium, galliumarsenide, glass, sapphire, and any other materials such as metals, metalnitrides, metal alloys, and other conductive materials, depending on theapplication. Substrates include, without limitation, semiconductorwafers. Substrates may be exposed to a pretreatment process to polish,etch, reduce, oxidize, hydroxylate, anneal, UV cure, e-beam cure and/orbake the substrate surface. In addition to film processing directly onthe surface of the substrate itself, in the present invention, any ofthe film processing steps disclosed may also be performed on anunderlayer formed on the substrate as disclosed in more detail below,and the term “substrate surface” is intended to include such underlayeras the context indicates. Thus for example, where a film/layer orpartial film/layer has been deposited onto a substrate surface, theexposed surface of the newly deposited film/layer becomes the substratesurface.

Embodiments of the disclosure provide methods of improving surfaceroughness of a flowable CVD film. Some embodiments advantageouslyprovide methods involving cyclic deposition-treatment processes that canbe performed in a cluster tool environment. Some embodimentsadvantageously provide seam-free high quality, low roughness films thatcan be used to fill up high aspect ratio (AR) trenches/features withsmall dimensions.

In one or more embodiments, surface treatment on a substrate surfacebefore flowable chemical vapor deposition (FCVD) advantageously improvesthe uniformity of the initial nucleation and improves overall smoothnessof the flowable CVD film. In one or more embodiments, plasma treatmentwith inert or reactive gases is found to be effective. In one or moreembodiments, the plasma pre-treatment is generated by a remote plasmasource (RPS) or a capacitively coupled plasma (CCP) or an inductivelycoupled plasma (ICP) with ambient like argon (Ar), helium (He), ammonia(NH₃), nitrogen (N₂), hydrogen (H₂), or their mixtures. In one or moreembodiments, initial nucleation smoothness can be further improved bychanging the order in which the reactants are introduced, changing theflow ratio of the reactants, and by changing the reactants retentiontime in the chamber during deposition.

In one or more embodiments, ending deposition of the flowable CVD filmis critical important for smooth deposition. In one or more embodiments,fast elimination of radical residues and avoiding reaction inunpreferred process regimes at the end of deposition reduces surfaceroughness significantly.

One or more embodiments of the disclosure are directed to processeswhere flowable CVD films are deposited which are able to fill highaspect ratio structures (e.g., AR>8:1). Embodiments of the disclosureprovide method of pre-treating a substrate surface prior to formation ofa flowable CVD film in order to form a smooth surface.

For descriptive purposes, the deposition of flowable CVD films forgapfill applications is described. However, those skilled in the artwill understand that the precursors and methods described are notlimited to gapfill applications and can be used for any flowable CVDfilm formation. FIG. 1 shows a partial cross-sectional view of asubstrate 100 with a feature 110. The Figures show substrates having asingle feature for illustrative purposes; however, those skilled in theart will understand that there can be more than one feature. The shapeof the feature 110 can be any suitable shape including, but not limitedto, trenches and cylindrical vias. As used in this regard, the term“feature” means any intentional surface irregularity. Suitable examplesof features include, but are not limited to trenches which have a top,two sidewalls and a bottom, peaks which have a top and two sidewalls.Features can have any suitable aspect ratio (ratio of the depth of thefeature to the width of the feature). In some embodiments, the aspectratio is greater than or equal to about 5:1, 10:1, 15:1, 20:1, 25:1,30:1, 35:1 or 40:1.

In one or more embodiments, the substrate 100 has a substrate surface120. The at least one feature 110 forms an opening in the substratesurface 120. The feature 110 extends from the substrate surface 120 to adepth D to a bottom surface 112. The feature 110 has a first sidewall114 and a second sidewall 116 that define a width W of the feature 110.The open area formed by the sidewalls and bottom are also referred to asa gap.

One or more embodiments of the disclosure are directed to processingmethods in which a substrate surface with at least one feature thereonis provided. As used in this regard, the term “provided” means that thesubstrate is placed into a position or environment for furtherprocessing.

As shown in FIG. 2, a flowable CVD film 150 is formed on the substratesurface 120 and the first sidewall 114, second sidewall 116 and bottomsurface 112 of the at least one feature 110. The flowable CVD film 150fills the at least one feature 110 so that substantially no seam isformed. A seam is a gap that forms in the feature between, but notnecessarily in the middle of, the sidewalls of the feature 110. As usedin this regard, the term “substantially no seam” means that any gapformed in the film between the sidewalls is less than about 1% of thecross-sectional area of the sidewall.

The flowable CVD film 150 can be formed by any suitable process. In someembodiments, the forming the flowable CVD film is done byplasma-enhanced chemical vapor deposition (PECVD). Stated differently,the flowable CVD film can be deposited by a plasma-enhanced chemicalvapor deposition process.

Embodiments of the disclosure advantageously provide methods ofpre-treating a substrate surface to form a smooth pre-treat substratesurface that can be use in deposition of flowable CVD films. In one ormore embodiments, a substrate surface is pre-treated with a plasma toform a smooth pre-treated substrate surface having chemical bondingsthat promote smoothness. A flowable CVD film is then formed on thepre-treated substrate surface by exposing the pre-treated substratesurface to a precursor and a reactant. The flowable CVD film is thencured.

In one or more embodiments, the plasma used to pre-treat the substratesurface comprises one or more of argon (Ar), helium (He), hydrogen (H₂),nitrogen (N₂), or ammonia (NH₃).

In one or more embodiments, pre-treating the substrate surface occurs ata pressure in a range of about 5 mTorr to about 100 mTorr. Pre-treatingthe substrate surface may occur at a temperature in a range of about 25°C. (or ambient temperature) to about 400° C.

Embodiments of the disclosure are directed to processing methodscomprising exposing a pre-treated substrate surface to a precursor and aco-reactant to deposit a flowable CVD film. In one or more embodiments,the precursor comprises trisilyamine (TSA). Thus, in one or moreembodiments, a substrate surface is pre-treated with a plasma, e.g.argon (Ar), helium (He), hydrogen (H₂), nitrogen (N₂), or ammonia (NH₃),and trisilylamine (TSA) is flowed over the pre-treated substratesurface. After TSA is flowed over the pre-treated substrate surface,ammonia (NH₃) is flowed over the substrate surface to form a flowableCVD film on the substrate surface. In one or more embodiments, the ratioof TSA/NH₃ is in a range of about 5:1 to about 30:1.

In one or more embodiments, flowing the TSA and flowing the NH₃ isconducted in the presence of oxygen (O₂). In one or more embodiments,oxygen (O₂) is present for the formation of silicon oxide (SiOx) films.In one or more embodiments, ammonia (NH₃) is present for the formationof silicon nitride (SiNx) films.

In other embodiments, the flowing the TSA and NH₃ is conductedsubstantially in the absence of oxygen (O₂). Stated differently, in oneor more embodiments the substrate surface is substantially free ofoxygen (O₂) when TSA and NH₃ are flowed over the substrate surface. Asused herein, the term “substantially in the absence of” or the term“substantially free of” means that there is less than 5%, including lessthan 4%, less than 3%, less than 2%, less than 1%, and less than 0.5% ofoxygen present in the atmosphere surrounding the substrate surface.

In one or more embodiments, flowing the TSA over the substrate surfaceto form the flowable CVD film on the substrate occurs at a pressure in arange of about 0.3 Torr to about 1 Torr. In one or more embodiments,flowing the TSA over the substrate surface to form the flowable CVD filmon the substrate (i.e. forming the treated substrate) occurs at atemperature in a range of about 25° C. (or ambient temperature) to about100° C.

In one or more embodiments, the flowable CVD film that is formed on thepre-treated substrate surface has at thickness in a range of about 5 nmto about 50 nm, including about 10 nm, about 15 nm, about 20 nm, about25 nm, about 30 nm, about 35 nm, about 40 nm, or about 45 nm. In one ormore embodiments, the flowable CVD film is ultra-thin and has athickness less than or equal to about 50 nm.

In some embodiments, the processing method further comprises eliminatingoxygen (O₂) from the substrate environment and turning off the flow ofammonia (NH₃), while continuing to flow triysilylamine (TSA) over thetreated substrate with flowable CVD deposition. Without intending to bebound by theory, it is thought that surface roughness of the flowableCVD film is improved with this termination process. In one or moreembodiments, atomic force microscopy (AFM) images show roughness isimproved by at least three to four times.

In one or more embodiments, the trisilyamine (TSA) precursor may bevaporized to a CVD chamber, and a suitable co-reactant (e.g., ammonia(NH₃), oxygen (O₂), carbon dioxide (CO₂), carbon monoxide (CO), argon(Ar), helium (He), hydrogen (H₂), or any combination thereof) can bedelivered to the chamber through, for example, a remote plasma source(RPS), which will generate plasma active species as the co-reactants.Plasma activated co-reactant molecules (radicals) have high energies andmay react with trisilylamine (TSA) precursor molecules in the gas phaseto form corresponding flowable polymers. In some embodiments, the plasmais generated with a plasma gas that comprises one or more of NH₃, O₂,CO₂, CO, Ar, He, or H₂.

In one or more embodiments, the plasma can be generated or ignitedwithin the processing chamber (e.g., a direct plasma) or can begenerated outside of the processing chamber and flowed into theprocessing chamber (e.g., a remote plasma).

Referring to FIG. 2, the flowable CVD film 150 can be formed at anysuitable temperature. In some embodiments, the flowable CVD film 150 isformed at a temperature in the range of about 10° C. to about 100° C.The temperature can be kept low to preserve the thermal budget of thedevice being formed. In some embodiments, forming the flowable CVD filmoccurs at a temperature less than about 300° C., 250° C., 200° C., 150°C., 100° C., 75° C., 50° C., 25° C. or 0° C.

The composition of the flowable CVD film can be adjusted by changing thecomposition of the reactive gas. In some embodiments, the flowable CVDfilm comprises one or more of silicon carbide (SiC), silicon oxycarbide(SiOC), silicon carbonitride (SiCN), silicon oxycarbonitride (SiOCN),silicon oxide (SiO) and silicon nitride (SiN). To form an oxygencontaining film, the co-reactant may comprise, for example, one or moreof oxygen, ozone or water. To form a nitrogen containing film, theco-reactant may comprise, for example, one or more of ammonia,hydrazine, NO₂ or N₂. To form a carbon containing film, the reactive gasmay comprise, for example, one or more of propylene and acetylene. Thoseskilled in the art will understand that combinations of or other speciescan be included in the reactive gas mixture to change the composition ofthe flowable CVD film.

The flowable CVD film may deposit on the wafer (temperature of the wafercan be from −10° C. to 200° C.) and due to their flowability, polymerswill flow through trenches and make a gap-fill. Then these films aresubjected curing steps such as ozone/UV/steam annealing/NH₃ annealing toget stable films. In one or more embodiments, after formation of theflowable CVD film 150, the film may be cured to solidify the flowableCVD film and form a substantially seam-free gapfill. In one or moreembodiments, curing the flowable CVD film comprises exposing theflowable CVD film to one or more of ozone, UV light, steam annealing,ammonia annealing and oxygen plasma. In some embodiments, the flowableCVD film is cured by exposing the film to a UV curing process. The UVcuring process can occur at a temperature in the range of about 10° C.to about 550° C. The UV curing process can occur for any suitable timeframe necessary to sufficiently solidify the flowable CVD film. The UVcure can be performed with different parameters, e.g., power,temperature, environment. In some embodiments, the UV cure occurs in anacetylene/ethylene environment.

In some embodiments, curing the flowable CVD film comprises thermalannealing. Thermal annealing can occur at any suitable temperature andany suitable environment. In some embodiments, the flowable CVD film iscured by thermal annealing in an acetylene/ethylene environment.

In some embodiments, curing the flowable CVD film comprises exposure toa plasma or an electron beam. A plasma exposure to cure the filmcomprises a plasma separate from the PECVD plasma. The plasma speciesand processing chamber can be the same and the plasma cure is adifferent step than the PECVD process.

In some embodiments, curing the flowable CVD film comprises exposing theflowable CVD film to a steam anneal and/or oxygen plasma. The use of asteam anneal and/or oxygen plasma may reduce the carbon content of theflowable CVD film so that the cured film has a lower carbon content thanthe as-deposited flowable CVD film. The use of steam anneal and/oroxygen plasma may convert the deposited flowable SiC, SiCN, or SiOC filmto SiO.

In some embodiments, the trisilylamine (TSA) precursor can be used withanother precursor (e.g. co-flow with another Si-containing precursor) ina flowable process to deposit films of various compositions. As anexample, precursors containing silicon and hydrocarbon groups can beused with the trisilylamine (TSA)/NH₃ process to incorporate carbon intothe flowable CVD film. In one or more embodiments, the flowable CVDfilms obtained from TSA/NH₃ process are either SiO or SiN films. By theaddition of a precursor containing carbon and silicon, SiOC, SiCON orSiCN films can be deposited.

In some embodiments, the flowable CVD film can be doped with anotherelement. For example, in one or more embodiments, the flowable CVD filmmay be doped with one or more of boron (B), arsenic (As), or phosphorous(P). The flowable CVD films can be doped with elements such as boron (B)and phosphorous (P) to improve film properties. Precursors containingboron and phosphorous can be either co-flowed with the trisilylamine(TSA) and ammonia (NH₃) precursors during the deposition process or canbe infiltrated after the deposition is done. Boron containing precursorscan be aminoboranes/boranes compounds and phosphorous containingprecursors can be phosphate/phosphite compounds. In some embodiments,doping the flowable CVD film comprises co-flowing a dopant precursorwith the trisilylamine (TSA) and ammonia (NH₃) precursors. In someembodiments, doping the flowable CVD film comprises implantation of thedopant element in a separate process.

According to one or more embodiments, the substrate is subjected toprocessing prior to and/or after forming the layer. This processing canbe performed in the same chamber or in one or more separate processingchambers. In some embodiments, the substrate is moved from the firstchamber to a separate, second chamber for further processing. Thesubstrate can be moved directly from the first chamber to the separateprocessing chamber, or it can be moved from the first chamber to one ormore transfer chambers, and then moved to the separate processingchamber. Accordingly, the processing apparatus may comprise multiplechambers in communication with a transfer station. An apparatus of thissort may be referred to as a “cluster tool” or “clustered system,” andthe like.

Generally, a cluster tool is a modular system comprising multiplechambers which perform various functions including substratecenter-finding and orientation, degassing, annealing, deposition, plasmatreatment, UV curing, and/or etching. According to one or moreembodiments, a cluster tool includes at least a first chamber and acentral transfer chamber. The central transfer chamber may house a robotthat can shuttle substrates between and among processing chambers andload lock chambers. The transfer chamber is typically maintained at avacuum condition and provides an intermediate stage for shuttlingsubstrates from one chamber to another and/or to a load lock chamberpositioned at a front end of the cluster tool. Two well-known clustertools which may be adapted for the present disclosure are the Centura®and the Endura®, both available from Applied Materials, Inc., of SantaClara, Calif. However, the exact arrangement and combination of chambersmay be altered for purposes of performing specific steps of a process asdescribed herein. Other processing chambers which may be used include,but are not limited to, cyclical layer deposition (CLD), atomic layerdeposition (ALD), chemical vapor deposition (CVD), physical vapordeposition (PVD), etch, pre-clean, chemical clean, thermal treatmentsuch as RTP, plasma nitridation, degas, orientation, hydroxylation andother substrate processes. By carrying out processes in a chamber on acluster tool, surface contamination of the substrate with atmosphericimpurities can be avoided without oxidation prior to depositing asubsequent film.

According to one or more embodiments, the substrate is continuouslyunder vacuum or “load lock” conditions, and is not exposed to ambientair when being moved from one chamber to the next. The transfer chambersare thus under vacuum and are “pumped down” under vacuum pressure. Inertgases may be present in the processing chambers or the transferchambers. In some embodiments, an inert gas is used as a purge gas toremove some or all of the reactants. According to one or moreembodiments, a purge gas is injected at the exit of the depositionchamber to prevent reactants from moving from the deposition chamber tothe transfer chamber and/or additional processing chamber. Thus, theflow of inert gas forms a curtain at the exit of the chamber.

The substrate can be processed in single substrate deposition chambers,where a single substrate is loaded, processed and unloaded beforeanother substrate is processed. The substrate can also be processed in acontinuous manner, similar to a conveyer system, in which multiplesubstrate are individually loaded into a first part of the chamber, movethrough the chamber and are unloaded from a second part of the chamber.The shape of the chamber and associated conveyer system can form astraight path or curved path. Additionally, the processing chamber maybe a carousel in which multiple substrates are moved about a centralaxis and are exposed to deposition, etch, annealing, cleaning, etc.processes throughout the carousel path.

During processing, the substrate can be heated or cooled. Such heatingor cooling can be accomplished by any suitable means including, but notlimited to, changing the temperature of the substrate support andflowing heated or cooled gases to the substrate surface. In someembodiments, the substrate support includes a heater/cooler which can becontrolled to change the substrate temperature conductively. In one ormore embodiments, the gases (either reactive gases or inert gases) beingemployed are heated or cooled to locally change the substratetemperature. In some embodiments, a heater/cooler is positioned withinthe chamber adjacent the substrate surface to convectively change thesubstrate temperature.

The substrate can also be stationary or rotated during processing. Arotating substrate can be rotated (about the substrate axis)continuously or in discrete steps. For example, a substrate may berotated throughout the entire process, or the substrate can be rotatedby a small amount between exposures to different reactive or purgegases. Rotating the substrate during processing (either continuously orin steps) may help produce a more uniform deposition or etch byminimizing the effect of, for example, local variability in gas flowgeometries.

Reference throughout this specification to “one embodiment,” “certainembodiments,” “one or more embodiments” or “an embodiment” means that aparticular feature, structure, material, or characteristic described inconnection with the embodiment is included in at least one embodiment ofthe disclosure. Thus, the appearances of the phrases such as “in one ormore embodiments,” “in certain embodiments,” “in one embodiment” or “inan embodiment” in various places throughout this specification are notnecessarily referring to the same embodiment of the disclosure.Furthermore, the particular features, structures, materials, orcharacteristics may be combined in any suitable manner in one or moreembodiments.

Although the disclosure herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent disclosure. It will be apparent to those skilled in the art thatvarious modifications and variations can be made to the method andapparatus of the present disclosure without departing from the spiritand scope of the disclosure. Thus, it is intended that the presentdisclosure include modifications and variations that are within thescope of the appended claims and their equivalents.

What is claimed is:
 1. A processing method comprising: pre-treating a substrate surface with a plasma to form a smooth pre-treated substrate surface; flowing trisilylamine (TSA) over the pre-treated substrate, followed by flowing ammonia (NH₃) to form a treated substrate, wherein flowing the TSA and NH₃ is conducted in the presence of oxygen (O₂); eliminating oxygen (O₂); turning off the flow of ammonia (NH₃), while continuing to flow TSA over the treated substrate; forming a flowable CVD film on the treated substrate surface by exposing the treated substrate surface to a precursor and a reactant; curing the flowable CVD film.
 2. The method of claim 1, wherein the plasma comprises one or more of argon (Ar), helium (He), hydrogen (H₂), nitrogen (N₂), or ammonia (NH₃).
 3. The method of claim 1, wherein pre-treating the substrate surface occurs at a pressure in a range of about 5 mTorr to about 100 mTorr.
 4. The method of claim 3, wherein pre-treating the substrate surface occurs at a temperature in a range of about 25° C. to about 400° C.
 5. The method of claim 1, wherein the ratio of TSA/NH₃ is in a range of about 5:1 to about 30:1.
 6. The method of claim 1, wherein forming the treated substrate occurs at a pressure in a range of about 0.3 Torr to about 1 Torr.
 7. The method of claim 6, wherein forming the treated substrate occurs at a temperature in a range of about 25° C. to about 100° C.
 8. The method of claim 1, wherein the flowable CVD film has a thickness in a range of about 5 nm to about 50 nm.
 9. A processing method comprising: pre-treating a substrate surface with a plasma to form a smooth pre-treated substrate surface; flowing trisilylamine (TSA) over the pre-treated substrate, followed by flowing ammonia (NH₃) to form a treated substrate; forming a flowable CVD film on the treated substrate by exposing the treated substrate to a precursor and a reactant, the flowable CVD film having a thickness in a range of about 5 nm to about 50 nm; curing the flowable CVD film; eliminating oxygen (O₂); and turning off the flow of ammonia (NH₃), while continuing to flow TSA over the treated substrate.
 10. The method of claim 9, wherein the ratio of TSA/NH₃ is in a range of about 5:1 to about 30:1.
 11. The method of claim 9, wherein flowing the TSA and NH₃ is conducted in the presence of oxygen (O₂).
 12. The method of claim 9, wherein flowing the TSA and NH₃ is conducted substantially in the absence of oxygen (O₂).
 13. The method of claim 9, wherein forming the treated substrate occurs at a pressure in a range of about 0.3 to about 1 Torr.
 14. The method of claim 13, wherein forming the treated substrate occurs at a temperature in a range of about 10° C. to about 100° C.
 15. A processing method comprising: pre-treating a substrate surface with a plasma to form a smooth pre-treated substrate surface; flowing trisilylamine (TSA) over the pre-treated substrate, followed by flowing ammonia (NH₃) and oxygen (O₂) to form a flowable CVD film having a thickness in a range of about 5 nm to about 50 nm; eliminating oxygen (O₂); turning off the flow of ammonia (NH₃), while continuing to flow TSA over the treated substrate; and curing the flowable CVD film. 